The microPET Focus 120 scanner is a third-generation animal PET scanner dedicated to rodent imaging. Here, we report the results of scanner performance testing. Methods: A 68 Ge point source was used to measure energy resolution, which was determined for each crystal and averaged. Spatial resolution was measured using a 22 Na point source with a nominal size of 0.25 mm at the system center and various off-center positions. Absolute sensitivity without attenuation was determined by extrapolating the data measured using an 18 F line source and multiple layers of absorbers. Scatter fraction and counting rate performance were measured using 2 different cylindric phantoms simulating rat and mouse bodies. Sensitivity, scatter fraction, and noise equivalent counting rate (NECR) experiments were repeated under 4 different conditions (energy window, 250;750 keV or 350;650 keV; coincidence window, 6 or 10 ns). A performance phantom with hot-rod inserts of various sizes was scanned, and several animal studies were also performed. Results: Energy resolution at a 511-keV photopeak was 18.3% on average. Radial, tangential, and axial resolution of images reconstructed with the Fourier rebinning (FORE) and filtered backprojection (FBP) algorithms were 1.18 (radial), 1.13 (tangential), and 1.45 mm full width at half maximum (FWHM) (axial) at center and 2.35 (radial), 1.66 (tangential), and 2.00 mm FWHM (axial) at a radial offset of 2 cm. Absolute sensitivities at transaxial and axial centers were 7.0% (250;750 keV, 10 ns), 6.7% (250;750 keV, 6 ns), 4.0% (350;650 keV, 10 ns), and 3.8% (350;650 keV, 6 ns). Scatter fractions were 15.9% (mouse phantom) and 35.0% (rat phantom) for 250;750 keV and 6 ns. Peak NECR was 869 kcps at 3,242 kBq/mL (mouse phantom) and 228 kcps at 290 kBq/mL (rat phantom) at 250;750 keV and 6 ns. Hot-rod inserts of 1.6-mm diameter were clearly identified, and animal studies illustrated the feasibility of this system for studies of whole rodents and mid-sized animal brains. Conclusion: The results of this independent field test showed the improved physical characteristics of the F120 scanner over the previous microPET series systems. This system will be useful for imaging studies on small rodents and brains of larger animals.Key Words: small-animal PET; performance measurement; instrumentation; molecular imaging; small-animal imaging PETi s a noninvasive, diagnostic imaging technique that produces functional or biochemical images of a body (1-4). Although PET is regarded as a powerful translational research tool between animal models and human clinical applications (5-8), clinical PET scanners used for human studies do not have satisfactory spatial resolution or sensitivity for studies of small animals, such as rats and mice (9-11). Because the linear dimensions of organs in these animals are 10 or more times smaller in each dimension than in human subjects, the spatial resolution of a suitable PET scanner must be similarly higher and the voxel size should also be reduced according to sampling theory (9,10). T...

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Our finding that tumor uptake of FLT was reduced at 24 h after radiation treatment suggests that FLT PET may be a promising imaging modality for monitoring the early effects of radiation therapy.